The bag cell neurons of the marine opisthobrance mollusk Aplysia, synthesize and release, when active, a number of polypeptides and peptides. One of these peptides, approximately pI9, m.w. 4500, induces egg-laying and correlated behavior when injected into reciepients. This neuropeptide, egg-laying hormone (ELH), has been purified and sequenced and is known to have direct effects on the central nervous system of Aplysia. We have generated antibodies to ELH for a variety of biochemical and physiological experiments: With ELH antibody and radioiodinated ELH, we play to quantitate levels of ELH in blood (during mating), during in vitro discharge of bag cells (BCs) and while isolating ELH from BC clusters. With the indirect fluorescene and immunoperoxidase techniques we can establish, by immunocytochemistry, whether ELH is synthesized in all BCs, how this changes with sexual maturity, the detailed morphology and location of BC processes and determine whether there are ELH-like cells in other parts of the CNS. With radioiodinated ELH we can begin to probe where the various target organs and receptors for ELH are located. The BC neurons in each cluster discharge synchronously on synaptic activation in vitro and afterdischarge for approximately 30 minutes (at 14 degrees Centigrade) after synaptic activation. Following such an afterdischarge, the BC neurons become refractory, for generating another long afterdischarge, for several hours. We propose to investigate the mechanisms by which the afterdischarge and subsequent refractoriness are generated using electrophysiological, pharmacological and biochemical techniques. Our present evidence indicates an increas e in cAMP during the early stage of afterdischarge and the removal of refractoriness for afterdischarge by phosphodiesterase inhibitors.